C. rostratum, Ehrenberg. (R. XXX.) Not common. Differs from C. setaceum in its greater size and in having the slender beaks shorter than the body of the frond. I show the two plants in figs. 34 and 35; is the distinction between them sufficient? C. acutum, Lyngbye. (R. XXX.) Rare. 14. Spirotænia, Brébisson. S. condensata, Brébisson. (R. XXXIV.) Not uncommon in spring. This plant is more affected than any other which I have seen by the fluids used for mounting or preserving. I have tried glycerine, camphor water, Ralfs' fluid, etc.; but they all shrivel up the endochrome considerably, and as the beauty and characters of Spirotœnia are quite lost unless the endochrome be uninjured, preserved specimens are useless. Distilled water even seems to have a bad effect. Almost all other Desmids stand mounting in glycerine well, but this is quite spoilt by it. 15. Ankistrodesmus, Corda. A. falcatus, Corda. (R. XXXIV.) Very common. A. acutissimus, Archer, (Qu. Journ., 1862). Rare. I had sometimes observed this plant and was struck by its peculiarities before meeting with Mr. Archer's description,* Quart. Journ. of Micr. Science,” Vol. II., New Ser., 1862. and had considered it a Closterium, but it evidently shows the oblique transverse band, and mediolateral (to coin a word) pale space referred to by Mr. Archer. The plant is very rare, and from its minute size (1/500 inch long, 1/10000 inch broad) requires a high power to examine it. Ankistrodesmus sp. indet. Figs. 17, 18. Common. I have frequently found specimens clearly belonging to this genus, but am doubtful as to its specific affinities. The cells are aggregated in bundles, but instead of crossing each other as in A. falcatus, they are arranged in parallel lines, and they are also only very slightly lunate, often quite straight. In some specimens I observed a definite mucous envelope enclosing four such parallel bundles as in fig. 17. Length of the cells, 1/660 inch; breadth, 1/7000 inch. Ankistrodesmus sp. indet. Figs. 19, 20.